Compression Levels, ZIP better than TAR-GZIP? XD

Hi Daniel, I’m testing deeply the plugin to obtain the best performance and generate the smallest possible backup attachments.
The question now is: what options are you using to set the compression level in TAR GZIP and with ZIP?
I found that a 6 MB SQL dump when sent as ZIP weighs 1 MB. But when I send the backup using TAR GZIP, it weighs 3 MB.

I always believed that TAR GZIP with its double compression should create smaller files. Isn’t it?